Liquid rosin size containing anti-stratifying and viscosity decreasing agent



tates LIQUID ROSIN SiZE CUNTAINING ANTI-STRATI- FYING AND VISCOSITYDECREASING AGENT John F. Gorham, Orono, Maine, Edward Strazdins,Stamford, Conn., William C. Hopkins, Valdosta, Ga., and John G. Senese,Jr., South Charleston, W. Va., assignors to American Cyanamid Company,New York, N. Y., a corporation of Maine No Drawing. Application February25, 1954 Serial No. 412,645

7 Claims. (Cl. 106-233) of the sizes, and substantially preventsstratification of the sizes on storage.

Rosin sizes have their principal use in the manufacture of paper. Thesesizes are manufactured on a large commercial scale by heating a naturalor modified rosin above its melting point, forming a hot causticsolution from water and an alkali metal alkali such as potassium or,more commonly, sodium hydroxide or carbonate, and reacting the alkalisolution with the rosin. The rosins referred to are organic acids.Neutralization of these acids by the caustic takes place within a fewhours, the product being a viscous soap dispersion. In this process, theamount of water employed is controlled so that the size contains betweenabout 50% and 80%-85 of solids, on the one hand to avoid sizes as dilutethat they cannot be shipped economically, and on the other hand to avoidsizes so concentrated and, therefore, viscous that they cannot bepumped.

The amount of alkali employed in this manufacture is at least about 60%of that required for complete neutralization so that the size containsabout 40% of free rosin acids, 21 lower amount of alkali yielding a sizewhich contains so much free rosin acids that it cannot be suc cessfullydiluted for application to paper. On the other hand, the amount ofalkali may be sufiicient to completely neutralize the rosin, and thisyields satisfactory sizes.

In commercial practice, liquid rosin sizes generally contain between 60%and 80% of solids by weight, thus minimizing shipping costs whileproviding a product having a pumpable viscosity at a temperature ofabout 60-70 C., this being the standard temperature at which sizes arehandled within paper mills. Moreover, sufficient alkali is used to causeat least 65 %75 neutralization of the rosin, this amount insuring thatthe rosin possesses excellent dilutability in water while maintainingconsumption of alkali and the viscosity of the product at minimumpractical values.

Frequently, liquid rosin sizes are stored by the manufacturer beforethey are shipped in tank cars, and these sizes are further stored bypaper manufacturers before use. It is known that during these periods ofstorage liquid rosin sizes of the commercially practicable typesmentioned, that is, sizes containing from about 5% to 25% of free rosinacids and about 60% to 80% of solids, stratify on storage and separateinto two layers. The bottom layer is more viscous than the upper layer.Hence, when a liquid rosin size has been prepared of maximum pumpableviscosity, allowance being made for the increase in viscosity whichnormally takes place on aging, storage of the size resultsin separationof a bottom layer which is beyond the range of normal pumpability andwhich,

2,832,693 Patented Apr. 29, 1958 "ice therefore, can be removed from thestorage tank only with difiiculty.

A further disadvantage is that the upper layer is usually darker incolor than the lower layer, and this introduces a problem of colorcontrol in the manufacture of paper.

Stratification of liquid rosin size often becomes evident in thelaboratory in 3-5 hours and, in the case of rosin stored in largecommercial tanks, in about 3 days. The phenomenon is not spontaneouslyreversible and homogeneity can be restored only by thorough mixing ofthe contents of the tank.

The discovery has now been made that liquid rosin sizes of thecomposition mentioned are much improved in terms of decreased viscosityby a dissolved content of between about /1 and 6% of alkali metalnitrate, based on the solids content of the size, that from about /2% toabout 2% inhibits Stratification, and that Stratification issubstantially completely prevented by the presence therein of betweenabout 2% and about 6% by weight of dissolved alkali metal nitrate basedon the weight of solids in the size. It has further been found thatseparation of the sizes into phases takes place when more than about 6%to 8% of the nitrate salt is present, the alkali metal nitrate in thisinstance acting to salt out the rosin soap resulting also in an actualincrease in viscosity of the size.

From the foregoing it will be seen that the subject matter of thepresent invention broadly comprises a liquid rosin size of about 5% to25% free rosin acids content containing about 60% to solids by weight,said size being improved by the presence ofan effective amount betweenabout /2% and 6% based on the weight of the solids, of an alkali metalnitrate dissolved therein.

The amount of alkali metal nitrate which should be present within therange mentioned to prevent stratilication varies with the type of rosinemployed, the solids content of the size, the amount of free rosin acidsin the size, and the temperature of the size. As a result, the minimumeffective amount can best be determined in each instance by laboratorytrial. In general, with regard to liquid rosin sizes of the compositionmentioned, we have found that fortified rosin sizes of low solidscontent but containing an intermediate amount of free rosin acids showthe greatest and most rapid stratification, and that with regard tothese sizes, higher temperatures favor Stratification. For example, afortified rosin size containing 60% or 70% solids and 15% of free rosinacids is particularly prone to stratify and requires somewhat more ofthe nitrate salt for stabilization at the upper normal storagetemperature of 80 C. than does ordinary rosin size containing 80% solidsand 15% free rosin acids at the lower normal storage temperature of 50C.

It is a particular advantage of the present invention that the presenceof only a small amount of alkali metal nitrate very greatly decreasesthe viscosity of the sizes often to only a small fraction of the valueswhich they would otherwise possess. Since the viscosity of liquid rosinsizes increases as their temperature falls, and since rosin sizes arenormally stored in heated storage tanks, this means that rosin in suchtanks can be stored at lower temperatures than would otherwise be thecase while still preserving the size at pumpable viscosity. It is thecurtomary practice of paper mills to store rosin size in tanksmaintained at a temperature between about 60-70 C. The presence of analkali metal nitrate permits the same sizes to be stored at atemperature about 20 C. lower without increase in viscosity, thuspermitting substantial economy in the heat supplied.

It is a further advantage that the alkali metal nitrate does not in anyway alter the color of the size or affect the usefulness of the size inthe manufacture of paper.

Freshly prepared liquid rosin size, when stored at normal temperatureswithin the range of 50-80 C. in-

mally produced on a very large industrial scale creases rapidly inviscosity during the course of about the first seven days, the viscosityat that time often being several times that of the initial viscosity ofthe material. Thereafter the viscosity of the size generally remains ator near the high value reached towards the end of the first week ofstorage. It is a further most important advantage that the action of thealkali metal nitrate is a permanent one, the stabilized sizes of thepresent invention having a much lower viscosity during and after thisperiod than corresponding sizes containing none of the nitrate.

In the manufacture of the liquid rosin sizes to which the presentinvention is directed, numerous forms of resin are currently employedand include gum rosin, wood rosin, and tall oil rosin, the latter beinga new development in the rosin field for which standards have beenpromulgated by the U. S. Department of Agriculture. Moreover, rosins maybe employed which contain a minor amount, e. g. to 40% by weight of theDiels-Alder adducts formed by reacting a naturally-occurring rosin withmaleic anhydride or similar material. These rosins and the sizesprepared therefrom, generally respectively termed fortified rosins andfortified rosin sizes are disclosed broadly in U. S. Patent Nos.2,628,918 and 2,385,794.

It will be understood that liquid rosin sizes, in addition to theforegoing, commonly contain a number of other materials. Included arethe lower aliphatic alcohols and rosin esters therewith since rosin sizemay be prepared from the latter. Moreover, natural rosins contain smallamounts of unsaponifiable materials including lignin and sterols. Sizescontaining these materials undergo stratification on storage and analkali metal nitrate is advantageously employed therewith.

The alkali metal nitrate may be introduced at any desirable point in themanufacture of the rosin size. For example, it may be dispersed into themolten rosin itself or may be dissolved in the liquid size subsequent toits preparation. Since, however, liquid rosin size is norit has beenfound most convenient to dissolve the nitrate in the water in which thealkali metal alkali is dissolved. In this manner uniform distribution ofthe anti-Stratification agent is most readily effected, and separatemetering of the agent becomes unnecessary.

In the present specification, the term percent free rosin acids is usedto designate the proportion of the rosin acids, as found by titration,which are not neutralized by the alkali-metal alkali during manufactureof the size.

The invention will be more particularly described with reference to theexamples which follow, which are intended only to illustrate specificembodiments of the invention and which are not to be construed aslimitations thereon.

Example 1 The effect of sodium nitrate in inhibiting stratification anddecreasing the viscosity of a liquid fortified rosin size is illustratedas follows.

A liquid fortified rosin size was prepared by heating 15,000 pounds of Mgrade gum rosin to 150 C. and slowly adding 600 pounds of maleicanhydride. Reaction of the maleic anhydride was complete in 3 hours atabout 170-180 C., the product being fortified rosin containing theDiels-Alder rosin maleic anhydride product.

In a separate vessel 1,800 pounds of sodium hydroxide was dissolved in23,700 pounds of water and the mixture heated to 95 C. The moltenfortified rosin and the hot caustic solution were separately butsimultaneously pumped into a cook tank and the mixture agitated byagitation of live steam from the bottom. Reaction of the caustic wascomplete in 2 hours. The resulting size 4 had a free rosin acids contentof 15% and a solids content of 70%.

Six samples were withdrawn. To five was added sufiicient of anapproximately saturated hot aqueous sodium nitrate solution to providesodium nitrate as shown in the table. The sixth sample was leftuntreated as control. The viscosities of the samples were thendetermined at 55 C. and 71 C. The samples were then stored at C. for 48hours and observed for stratification.

Stratification was deemed to take place when two distinct layers couldbe observed. The samples were rated on an arbitrary scale on which 4indicates bad Stratification, 1 indicates acceptably slightStratification,

and 0 indicates no noticeable stratification. Results are as follows:

Viscosity (on) Stratifica- Percent at tion on Size NaNOa 1 Storage for48 Home at 55 0. 71 C 71 0.

None 16,600 3,340 4 o. 5 10, 900 1, 635 4 1. 0 7, 780 1, 2+ 1.5 7,2001,154 1+ 2.5 2, 800 1,000 0 3.0 2, 300 602 0 1 Based on solids contentof size.

These tests show that the presence of a very minor amount of sodiumnitrate caused a major decrease in viscosity, and that about 2%substantially prevented Stratification.

Example 2 The effect of potassium nitrate upon the viscosity andstratification of rosin size is illustrated by the following.

A fortified rosin size containing 70% solids and 19% free rosin acidswas made by the method of Example 1, the amount of caustic beingdecreased to 1,720 pounds, and a control sample and a potassiumnitrate-containing sample were prepared and tested as described in Ex- 1Based on the weight of solids in the size. 1 Centipoises.

In this case the amount of stratification was very minor, the lowerlayer being less than one-tenth the weight of the upper. The dataindicate that the maximum viscosity of the size which containedpotassium nitrate was lower than the initial viscosity of the controlsample.

We claim:

1. A liquid rosin size of from about 5% to 25% free rosin acids contentcontaining between about 60% and 80% of solids by weight, said sizecontaining an elfective amount between about /2% and 6%, based on theweight of said solids, of a dissolved alkali metal nitrate as agentdecreasing the viscosity of the size.

2. A size according to claim 1 wherein the nitrate is sodium nitrate.

3. A liquid rosin size according to claim 1 containing a rosin-maleicanhydride adduct.

4. A liquid rosin size of from about 5% to 25% free rosin acids contentcontaining between about 60% to 80% of solids by weight, said size beinginhibited against stratification on storage by the presence of aneffective 7. A liquid rosin size according to claim 6 containing amountbetween about 2% and 6%, based on the weight a rosin-maleic anhydrideadduct. of said solids, of a dissolved alkali metal nitrate.

5. A liquid rosin size according to claim 4 containing References Citedin the file of this Patent a rosin-maleic anhydride adduct. 5 UNITEDSTATES PATENTS 6. A liquid rosin size of about 15% free rosin acids 2content containing about 70% of solids by weight, said gggig :32? gfif'g size containing an effective amount between 16% and n 6%, based on theweight of said solids, of a dissolved FOREIGN PATENTS alkali metalnitrate as agent decreasing the viscosity 10 15,269 Great Britain 1897of the size. v

1. A LIQUID ROSIN SIZE OF FROM ABOUT 5% TO 25% FREE ROSIN ACIDS CONTENTCONTAINING BETWEEN ABOUT 60% AND 80% OF SOLIDS BY WEIGHT, SAID SIZECONTAINING AN EFFECTIVE AMOUNT BETWEEN ABOUT 1/2% AND 6%, BASED ON THEWEIGHT OF SAID SOLIDS, OF A DISSOLVED ALKALI METAL NITRATE AS AGENTDECREASING THE VISCOSITY OF THE SIZE.